Coupling For Downhole Tools

ABSTRACT

Transferring rotary power between a first rotating member and a second rotating member may performed by using a first element associated with the first rotating member; and a second element associated with the second rotating member. The first element and the second element may be configured to rotate the first rotating member either substantially synchronously or non-synchronously with the second rotating member. A hysteresis material may be utilized in either or both of the first element and the second element. A modulator may be used to control a speed of the first element or the second element.

CROSS-REFERENCE TO RELATED APPLICATIONS Background of the Disclosure

1. Field of the Disclosure

This disclosure relates generally to oilfield downhole tools and more particularly to methods and devices for transferring a rotary motion to a consumer.

2. Description of the Related Art

To obtain hydrocarbons such as oil and gas, boreholes or wellbores are drilled by rotating a drill bit attached to the bottom of a BHA (also referred to herein as a “Bottom Hole Assembly” or (“BHA”). The BHA is attached to the bottom of a tubing, which is usually either a jointed rigid pipe or a relatively flexible spoolable tubing commonly referred to in the art as “coiled tubing.” The string comprising the tubing and the BHA is usually referred to as the “drill string.” When jointed pipe is utilized as the tubing, the drill bit is rotated by rotating the jointed pipe from the surface and/or by a mud motor contained in the BHA. In the case of a coiled tubing, the drill bit is rotated by the mud motor. BHA's, as well as other wellbore devices, may often incorporate equipment that require the transfer of rotary power from a generator to a consumer; e.g., from a turbine to an oil pump. The transfer of such rotary power often occurs across two or more rotating members such as shafts. Conventional couplings or gears may utilize magnetic contact between input side and output side. The couplings may utilize Permanent Magnet Synchronous Couplings (PMSC). Such couplings have input drive and an output drive coupled magnetically by using permanent magnets. As long as the maximum torque is not exceeded, both parts of the coupling run synchronously. When the torque is exceeded, the coupling de-couples such that no meaningful rotary power is conveyed across the coupling.

The present disclosure addresses the need for couplings that provide enhanced control over the transfer of rotary power between two or more rotating elements.

SUMMARY OF THE DISCLOSURE

In aspects, the present disclosure provides an apparatus for transferring rotary power between a first rotating member and a second rotating member. In one embodiment, the apparatus may include a first element associated with the first rotating member; and a second element associated with the second rotating member. The first element and the second element may be configured to rotate the first rotating member either substantially synchronously or non-synchronously with the second rotating member. In arrangements, a magnetic field may connect the first element with the second element. Also, the first rotating member and the second rotating member may shift from a synchronous rotation to a non-synchronous rotation when a predetermined torque value is applied by the first rotating member to the second rotating member. In arrangements, the apparatus may include a modulator that controls a rotational speed of the second rotating member. The modulator may reduce a strength of a magnetic field connecting the first element and the second element. In some applications, the modulator may be an eddy current brake connected to the second rotating member, an oil-pump and nozzle, or an additional load imposed by a consumer such as an alternator. In embodiments, the first element circumferentially surrounds the second element. Also, the second rotating member may be substantially isolated from a drilling fluid. In arrangements, the first element and the second element may be further configured to rotate the second rotating member at a substantially constant speed that is greater than zero when the first rotating member rotates non-synchronously with the second rotating member.

In aspects, the present disclosure provides a method for transferring rotary power between a first rotating member and a second rotating member. The method may include coupling the first rotating member to the second rotating member, rotating the first rotating member substantially synchronously with the second rotating member; and rotating the first rotating member substantially non-synchronously with the second rotating member when the first rotating member exceeds a specified rotary speed. In embodiments, the method may include rotating the second rotating member at a substantially constant speed after the first rotating member exceeds the specified rotary speed. The method may also include rotating the first rotating member at a speed greater than the substantially constant speed. The coupling may utilize a magnetic field and the method may include shifting the first rotating member and the second rotating member from a synchronous rotation to a non-synchronous rotation when a predetermined torque value is applied by the first rotating member to the second rotating member. Illustrative methods may further include modulating a rotational speed of the second rotating member. The modulating may reduce a magnetic field connecting the first element and the second element. The method may further include substantially isolating the second rotating member from a drilling fluid. In arrangements, the method may include rotating the second element at a substantially constant speed that is greater than zero when the first element rotates non-synchronously with the second element.

In embodiments, the present disclosure provides a system for transferring rotary power. The system may include a rotary power generator having a first rotating member, a consumer having a second rotating member, and a coupling connecting the first rotating member to the second rotating member. The coupling may be configured to rotate the first rotating member substantially synchronously and non-synchronously with the second rotating member. Either the first rotating member or the second rotating member may include a hysteresis material. In arrangements, a magnetic field connects the first rotating member and the second rotating member. Also, the first rotating member and the second rotating member may shift from a synchronous rotation to a non-synchronous rotation when a predetermined torque value is applied by the first rotating member to the second rotating member. In arrangements, the system may include a modulator that controls a rotational speed of the second rotating member. The modular may reduce a magnetic field connecting the first rotating member and the second rotating member.

Illustrative examples of some features of the disclosure thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the disclosure that will be described hereinafter and which will form the subject of the claims appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

For detailed understanding of the present disclosure, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein:

FIG. 1 illustrates a drilling system made in accordance with one embodiment of the present disclosure;

FIG. 2 illustrates in sectional schematic a coupling made in accordance with one embodiment of the present disclosure;

FIG. 3 graphically illustrates exemplary response curves for couplings made in accordance with embodiments of the present disclosure;

FIG. 4 illustrates in schematic format a coupling having a modulator in accordance with one embodiment of the present disclosure;

FIG. 5 schematically illustrates an eddy current modulator made in accordance with one embodiment of the present disclosure; and

FIG. 6 schematically illustrates a sectional view of a mechanical gearing system that utilizes hysteresis material in accordance with one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure relates to devices and methods for selectively coupling a driving rotating member to a driven rotating member. The present disclosure is susceptible to embodiments of different forms. The drawings show and the written specification describes specific embodiments of the present disclosure with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure, and is not intended to limit the disclosure to that illustrated and described herein.

As will be apparent from this disclosure, the present teachings provide enhanced control over connections between two or more rotating members. While the present teachings may be advantageously applied to any number of applications, for clarity and ease of explanation, reference will be made to FIG. 1, which shows a wellbore tool that may incorporate one or more components that require a connection between two components that rotate relative to one another. The FIG. 1 tool may incorporate one or more devices where a rotation parameter (e.g., speed or torque) of a rotating element should be maintained below a predetermined level or within a prescribed range. For instance, to reduce the likelihood of an over-voltage, it may be desirable to prevent the rotating element of a power generator, such as an alternator, from exceeding a specified rotational speed. Similarly, it may be desirable to limit the maximum rotating speed of a drive shaft for a pump to maintain fluid pressures or flow rates within a specified range. In still other situations, it may be useful to allow non-synchronous motion between a power source and a consumer to avoid problems caused by torsional vibrations. In aspects, embodiments of the present disclosure provide two operating modes: synchronous and non-synchronous. In the synchronous mode a maximum synchronous torque of the coupling is not exceeded. The torque in this mode is determined by a consumer. In the non-synchronous mode the maximum synchronous torque of the coupling is exceeded. Couplings made in accordance with the present disclosure operate such that the speed of the consumer will adjust automatically to a reduced speed (equilibrium of torque) so that the “Slipping-Torque” fits to the “slipping speed”. The “slipping speed” is the difference of input speed and output speed. In applications where the consumer does not fit to the desired effect (e.g., if the torque of the consumer decreases when the speed increases), then an additional suitable brake device may be utilized.

In FIG. 1, there is shown an embodiment of a drilling system 10 utilizing a bottomhole assembly (BHA) 60 configured for drilling wellbores. While a land system is shown, the teachings of the present disclosure may also be utilized in offshore or subsea applications. In FIG. 1, a laminated earth formation 10 is intersected by a well bore 12. A drilling system 30 having a bottom hole assembly (BHA) or drilling assembly 40 is conveyed via a tubing 42 into the wellbore 12 formed in the formation 10. The tubing 42 may be jointed drill pipe or coiled tubing, which may include embedded conductors for power and/or data for providing signal and/or power communication between the surface and downhole equipment. The communication system for transmitting uplinks and downlinks may include mud-driven power generation units (mud pursers), or other suitable two-way communication systems that use hard wires (e.g., electrical conductors, fiber optics), acoustic signals, EM or RF. The BHA 40 may include a drilling motor 44 for rotating a drill bit 46. In a common mode of operation, a pressurized drilling fluid is pumped down to the BHA 40 from the surface via the tubing 42. This flowing drilling fluid may be utilized to energize turbines or other similar devices that extract energy from the flowing drilling fluid. The extracted energy may be utilized to generate electricity and/or pressure hydraulic fluids. It should be understood that power generation and pressuring of fluids are merely illustrative of a variety of functions that may be performed by a consumer of energy transmitted via rotary motion. Other devices that may be present, but not shown, along the BHA 40 may include a steering assembly for steering the drill bit 46 in a selected direction, one or more BHA processors, one or more stabilizers, and other equipment known to those skilled in the art. The drill bit 46 may be rotated in any one of three modes: rotation by only the tubing 42, rotation by only the drilling motor 44, and rotation by a combined use of the tubing 42, and drilling motor 44. The BHA 40 also includes a logging tool 50, which may include a suite of tool modules, that obtain information relating to the geological, geophysical and/or petrophysical characteristics of the formation 10 being drilled. The subsurface components will be collectively referred to as a drill string 60.

Referring now to FIG. 2, there is shown an exemplary coupling 100 that may provide enhanced control over the transmission of rotary power between two or more components in the drill string 60 of FIG. 1. The coupling 100 may be configured to ensure that a parameter such as torque or speed is kept below a preset value, within a preset range, or controlled in some other prescribed manner. For example, the coupling 100 may be configured to operate in a synchronous mode and a non-synchronous mode. By synchronous, it is meant that rotational speed of the input section 110 substantially matches the rotational speed of the output section 120 or these rotational speeds are fixed by a specified ratio. By non-synchronous, it is meant that there is a mismatch between the rotational speeds of the input section 110 and the output section 120 or that an output speed no longer correspond to a fixed ratio with the input speed. Typically, in a non-synchronous mode, the output section 120 rotates at a speed that is slower than the speed of the input section 110.

In one embodiment, the coupling 100 transfers rotary power from the driving or input section 110 to the driven or output section 120. In embodiments, the sections 110 and 120 may include flexible shafts, tubes, rods or other suitable tubular rotary power transmission elements. The driving or input section 110 may include an energy source such as a turbine 112 that is energized by a flow of drilling fluid. The driving section 110 may also be energized by the rotation of the drill string or drill bit. A load 130, which may be an oil pump 132, is coupled to output section 120 via a shaft 122.

Referring now to FIG. 3, there is shown in several illustrative response curves for the coupling 100 shown in FIG. 2. The input speed is along the X-axis and the output speed is along the Y-axis. Line 140 illustrates one exemplary response curve of the coupling 100. The region labelled 142 may be considered the synchronous mode of operation wherein the rotary speed of the input section 110 and the output section 120 are about the same. At point 144, the input section 110 and the output section 120 shift from synchronized rotation to non-synchronized rotation. At this point the maximum synchronous torque of the coupling is reached and the coupling begins to slip. Specifically, the output section 120 no longer rotates at the same speed as the input section 110. The region of non-synchronous operation is shown with numeral 146. As a purely arbitrary range, the non-synchronous region may be between one-hundred RPM and two-hundred RPM. As the rotational speed of the input section 110 varies between this speed range, the output section 120 may provide a substantially stable and non-changing torque value. It should be understood that line 140 represents only one of numerous responses that may be exhibited by the coupling 100. For example, line 148 illustrates a non-synchronous mode wherein the torque output of the output section 120 increases with rotational speed, but at a different rate than the rate along the synchronous region 142. In another example, line 150 shows a non-linear torque output response wherein the torque decreases with the increase in rotational speed of the input section 110. Also, at point 152, the input section 110 may completely uncouple from the output section 120 such that the torque output drops to effectively a zero value.

It should therefore be appreciated that the coupling 100 provides meaningful or operation rotary power transfer across an extended rotary speed range. Moreover, the speed may be controlled such that the consumer is not driven at an undesirable speed. While two speed ranges are shown, it should be understood that the coupling 100 may be configured to have three or more operating speeds. That is, in a first input speed range, output speed may vary directly with input speed, in a second input speed range, a first steady output speed is maintained; in a third input speed range, a second steady output speed is maintained, etc.

In embodiments, the values for the transition value at point 144 and the total or complete decoupling at point 152 may be selected based on the operation characteristics or limitations of the load 140. As noted previously, the load 140 may be any consumer of rotary power such as an alternator that generates electricity, an oil pump that supplies pressurized fluid, or a cutting tool that uses rotary power to disintegrate a formation, a wall of a wellbore tubular, or any other material found in a wellbore.

Referring now to FIG. 2, in one embodiment, the coupling 100 may include a hysteresis ring 102 that rotates with the input section 110 and permanent magnet elements 104 that rotate with the output section 120. In arrangements, the hysteresis ring 102 may include one or more elements made of a hysteresis material. A hysteresis material may have typical magnetic properties: e.g., the coercive field strength that is relatively low, and the remanence and the permeability that are high. Illustrative materials include, but are not limited to, AlNiCo or FeChrCo. AlNiCo is relatively corrosion-resistant and has magnetic properties that are relatively independent with respect to temperature. The material may be magnetic isotropic or non-isotropic. If the material is non-isotropic (in the right direction) the torque of the coupling can be strongly increased. Suitable hysteresis material may be obtained from ARNOLD-SPS TECHNOLOGIES.

In some embodiments, an electrically conductive material may used as the hysteresis material. Such material may display or exhibit a torque characteristic associated with eddy current coupling. This torque characteristic may be reduced or eliminated through known lamination techniques, e.g., like a winding stack of an electrical motor or alternator.

Referring now to FIG. 2, it should be appreciated that the coupling 100 allows the input section 110 to be mechanically separated or otherwise isolated from the output section 120. As shown, the input section 110 is positioned in a region 133 through which drilling fluid may flow. Advantageously, the output section 120 may be sealed off or otherwise isolated from this drilling fluid with a fluid barrier 135 that may be fixed relative to the drill string. Furthermore, in the non-synchronous mode, the hysteresis ring 102 will radiate energy in the form of thermal energy (heat). Thus, in embodiments, the hysteresis ring 102 may be partially or completely immersed in or otherwise thermally coupled to the flowing drilling fluid in order to dissipate that thermal energy. Additionally, the positioning of the hysteresis ring 102, rather than the permanent magnetic elements 104, in the fluid reduces the amount of magnetic particles in the drilling fluid that are collected in the vicinity of the coupling 100, as opposed to an arrangement wherein the permanent magnet 104 is positioned in the flowing drilling fluid. Also, the polarization of the material changes in the non-synchronous mode further reduces the risk of collection of magnetic particles from the drilling fluid.

Referring now to FIG. 4, there is shown an embodiment of a coupling 100 that may utilize a modulator 160 for modulating the speed of the output drive 120. In embodiments, the modulator 160 may be utilized to control an operating characteristic of the load 120. Exemplary characteristics include, but are not limited to, speed and torque. Exemplary forms of control may include maintaining a substantially constant output speed, controlling a rate of increase in output speed, etc.

In one embodiment, the modulator 160 may be configured to control or rectify a rotary speed of the output shaft 122. The modular 160 may include a winding section 162, a permanent magnet section 163 that surrounds the winding section 162, and coils 164 that are electrically coupled to the winding section 162. In this case, the winding section 162 rotates inside a stationary permanent magnet section 160. In embodiments, a rotating rectifier 166 may be utilized to rectify the AC-Current of the winding section 162 before leading it to the coils 164. In other arrangements, the current may be regulated via electronics (either rotating or non-rotating) before leading it to the coils (not shown). The rotation of the shaft 122 causes the windings section 162 to generate a voltage that is applied to the coils 164. In response to the applied voltage, the coils 164 produce a magnetic field that weakens the field of the permanent magnets 104. Weakening the magnetic field of the permanent magnets 104 reduces the magnetic torque capability between the hysteresis ring 102 and permanent magnets 104. The reduced strength of the magnetic field shifts the point of de-synchronization to lower torque between the input section 110 and the output section 120. The magnitude of the voltage is dependent on the speed of the shaft 122; e.g., the voltage varies directly with the rotation speed. Therefore, as the speed of the output section 120 increases, the differential in the rotational speeds of the input section 110 and the output section 120 increases due to the increased slippage. It should be appreciated that appropriate configuration of the modulator 160 may yield a relatively constant input speed for the shaft 122 that drives the load 124.

Referring now to FIG. 5, the modulator may be in the form of an eddy current brake 170 that controls output speed by progressive applying increasing amount of torque as output speed increases. The brake 170 may include a housing 172, one or more magnetic elements 174 and a biased sleeve 176. The housing 172 may be formed of a metal suitable for creating eddy current, such as copper alloy, and may utilize other materials such as iron. A gap 178 separates an inner surface of the housing 172 from the radially outer surfaces of the magnetic elements 174. The magnetic elements 174 may be positioned on wings or support members 180 that may move a limited amount in the radial direction. The magnetic elements 174 may be positioned on the rotation shaft 122. The sleeve 176 may be configured to retain the support members 180 and their associated magnetic elements 174 in a nominal radially inward position. During operations, the rotation of the shaft 122 produces centrifugal forces that urge the wings 180 radially outward. This radial outward movement reduces the gap 178, which increases the magnetic flux in the housing 172. This magnetic flux, thus, applies increased braking forces on the shaft 122 to control the rotational speed of the shaft 122. Therefore, in embodiments, speed variance or modulation may be provided by reducing an air gap between the rotating and non-rotating components of the eddy current brake by using centrifugal force.

Referring now to FIG. 6, there is shown another exemplary coupling 190 that utilizes magnetic gearing to provide enhanced control over the transmission of rotary power between two or more components in the drill string 60 of FIG. 1. As in the previously-described embodiments, the coupling 190 may be configured to ensure that a parameter such as torque or speed is kept below a preset value, within a preset range, or controlled in some other prescribed manner. In one embodiment, the coupling 190 may include a hysteresis ring 192 that rotates with the input section 200 and permanent magnet elements 196 that rotate with the output section 194. Advantageously, the output section 120 may be sealed off or otherwise isolated from this drilling fluid with a fluid barrier 198. In arrangements, the hysteresis ring 192 may include one or more elements made of a hysteresis material as previously discussed. Rotational force is conveyed via the magnetic attraction between the permanent magnet elements 196 and the hysteresis ring 192. The permanent magnet elements 196 may be in segmented form and arranged to have alternating polarity. During synchronous operation, the rotational speed of the input section 200 is fixed relative to the rotational speed of the output section 194. During non-synchronous operation, the output section 194 “slips” relative to the input section 200. The slipping may be controlled such that the output speed remains constant even as the input speed exceeds a predetermined threshold.

Additional modulator may include an oil-pump that pumps fluid through a flow restriction element such as a nozzle, an alternator that may be load-controlled by electronics in addition to the required output power just to limit the speed; and any other devise that exhibit a strong progressive torque versus speed.

From the above, it should be appreciated that what has been described includes, in part, an apparatus for transferring rotary power between a first rotating member and a second rotating member. The rotary power may be generated by any suitable generator and the rotary power may be utilized, either directly or indirectly, by a variety of downhole power consumption devices. The apparatus may include a first element associated with the first rotating member; and a second element associated with the second rotating member. The first element and the second element may be configured to rotate the first rotating member either substantially synchronously or non-synchronously with the second rotating member. In arrangements, a magnetic field may connect the first element with the second element. Also, the first rotating member and the second rotating member may shift from a synchronous rotation to a non-synchronous rotation when a predetermined torque value is applied by the first rotating member to the second rotating member. In arrangements, the apparatus may include a modulator that controls a rotational speed of the second rotating member. The modulator may reduce a strength of a magnetic field connecting the first element and the second element. In some applications, the modulator may be an eddy current brake connected to the second rotating member, an oil-pump and nozzle, or an additional alternator load. In embodiments, the first element circumferentially surrounds the second element. Also, the second rotating member may be substantially isolated from a drilling fluid. In arrangements, the first element and the second element may be further configured to rotate the second rotating member at a substantially constant speed that is greater than zero when the first rotating member rotates non-synchronously with the second rotating member.

From the above, it should be appreciated that what has been described includes, in part, a method for transferring rotary power between a first rotating member and a second rotating member. The method may include coupling the first rotating member to the second rotating member, rotating the first rotating member substantially synchronously with the second rotating member; and rotating the first rotating member substantially non-synchronously with the second rotating member when the first rotating member exceeds a specified rotary speed. In embodiments, the method may include rotating the second rotating member at a substantially constant speed after the first rotating member exceeds the specified rotary speed. The method may also include rotating the first rotating member at a speed greater than the substantially constant speed. The coupling may utilize a magnetic field and the method may include shifting the first rotating member and the second rotating member from a synchronous rotation to a non-synchronous rotation when a predetermined torque value is applied by the first rotating member to the second rotating member. Illustrative methods may further include modulating a rotational speed of the second rotating member. The modulating may reduce a magnetic field connecting the first element and the second element. The method may further include substantially isolating the second rotating member from a drilling fluid. In arrangements, the method may include rotating the second element at a substantially constant speed that is greater than zero when the first element rotates non-synchronously with the second element.

From the above, it should be appreciated that what has been described includes, in part, a system for transferring rotary power. The system may include a rotary power generator having a first rotating member, a consumer having a second rotating member, and a coupling connecting the first rotating member to the second rotating member. The coupling may be configured to rotate the first rotating member substantially synchronously and non-synchronously with the second rotating member. Either the first rotating member or the second rotating member may include a hysteresis material. In arrangements, a magnetic field connects the first rotating member and the second rotating member. Also, the first rotating member and the second rotating member may shift from a synchronous rotation to a non-synchronous rotation when a predetermined torque value is applied by the first rotating member to the second rotating member. In arrangements, the system may include a modulator that controls a rotational speed of the second rotating member. The modular may reduce a magnetic field connecting the first rotating member and the second rotating member.

The foregoing description is directed to particular embodiments of the present disclosure for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope of the disclosure. It is intended that the following claims be interpreted to embrace all such modifications and changes. 

1. An apparatus for transferring rotary power between a first rotating member and a second rotating member, comprising: a first element associated with the first rotating member; and a second element associated with the second rotating member, the first element and the second element being configured to rotate the first rotating member substantially synchronously and non-synchronously with the second rotating member.
 2. The apparatus of claim 1 wherein one of the first element and the second element includes a hysteresis material.
 3. The apparatus of claim 1 wherein a magnetic field connects the first element and the second element, the first and the second element being configured to shift wherein the first rotating member and the second rotating member from a synchronous rotation to a non-synchronous rotation when a predetermined torque value is applied by the first rotating member to the second rotating member.
 4. The apparatus of claim 1 further comprising a modulator configured to control a rotational speed of the second rotating member.
 5. The apparatus of claim 4 wherein the modulator is configured to reduce a magnetic field connecting the first element and the second element.
 6. The apparatus of claim 4 wherein the modulator is one of: (i) an eddy current brake connected to the second rotating member, (ii) an oil-pump and nozzle; and (iii) an additional alternator load.
 7. The apparatus of claim 1 wherein the first element circumferentially surrounds the second element.
 8. The apparatus of claim 1 wherein the second rotating member is substantially isolated from a drilling fluid.
 9. The apparatus of claim 1 wherein the first element and the second element are further configured to rotate the second rotating member at a substantially constant speed that is greater than zero when the first rotating member rotates non-synchronously with the second rotating member.
 10. A method for transferring rotary power between a first rotating member and a second rotating member, comprising: coupling the first rotating member to the second rotating member; rotating the first rotating member substantially synchronously with the second rotating member; and rotating the first rotating member substantially non-synchronously with the second rotating member when the first rotating member exceeds a specified rotary speed.
 11. The method of claim 10, further comprising: rotating the second rotating member at a substantially constant speed after the first rotating member exceeds the specified rotary speed.
 12. The method of claim 11 further comprising rotating the first rotating member at a speed greater than the substantially constant speed.
 13. The method of claim 10, wherein the coupling is via a magnetic field; and further comprising: shifting the first rotating member and the second rotating member from a synchronous rotation to a non-synchronous rotation when a predetermined torque value is applied by the first rotating member to the second rotating member.
 14. The method of claim 10 further comprising a modulating a rotational speed of the second rotating member.
 15. The method of claim 14 wherein the modulating reduces a magnetic field connecting the first element with the second element.
 16. The method of claim 10 further comprising substantially isolating the second rotating member from a drilling fluid.
 17. The method of claim 10 further comprising rotating the second element at a substantially constant speed that is greater than zero when the first element rotates non-synchronously with the second element.
 18. A system for transferring rotary power, comprising: a rotary power generator having a first rotating member; a consumer having a second rotating member; and a coupling connecting the first rotating member to the second rotating member, the coupling being configured to rotate the first rotating member substantially synchronously and non-synchronously with the second rotating member.
 19. The system of claim 18 wherein one of the first rotating member and the second rotating member includes a hysteresis material.
 20. The system of claim 18 wherein a magnetic field connects the first rotating member and the second rotating member, and wherein the first rotating member and the second rotating member shift from a synchronous rotation to a non-synchronous rotation when a predetermined torque value is applied by the first rotating member to the second rotating member. 